Electrolytic recording



UNITED STATES PATENT "OFFICE ELECTROLYTIC RECORDING John V. L. Hogan, Forest Hills, Hugh C. Ressler,

West Brighton, and William H. Triblile, Brooklyn, N. Y., assignors, by mesne assignments, to Faxlmile, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application April 15, 1940, Serial No. 329,828

1 Claim.

The present invention concerns materials for, and processes of electrolytic recording.

One object ofthe present invention is to provide methods of preparing recording carriers or sheets which will keep substantially unaltleseg 5 zililsadvantiage? iiequires alditiona; spacte o: for long periods prior to recording and w c erecor er or e mpregnamg equi men will yield records which will not fade or discolor fiquires attiontiion t? mail'iligli'iillqlillith levelis, Etc. for long periods after recording. 0st impor an as ar as e nis e pro no is Another object is to increaie thefsliarpnefss of lo t ed; gs ti e {g t that mrggi ii gfi zuqi 11 recorded images by preven ing r nges rom Suppor Jus pr or ma n es forming during and after the instant of recordp on dlilstriibuttiolili andi conttrol ofnoisture in the ing. recor s cc a e pan 0 mar mg.

A further object is to provide an electrolytic The present invention concerns processes of recording material which is easily and cheaply p nati n in wh h t paper or other a i r prepared and which will yield superior recordis ttir cfi orrll isgaocessfdt tlotprlolcirclgerggnbdisizgings. u Ono 0 ecne e A still further object is to provide a process of Justed toany des ed Po t j W Sufi eient and material for recording electrolytically which time available, Paper Which Is e I S D O S will produce a dense, sharp and permanent mark a 119M118 a i h Wet St ength may be used as against a contrasting or white sheet at a high 21 i l llzg l ge gg a iri g eygigfilndlst gfgigogg rate of linear recording speed. 8 y g a I The a th objects win b evi from record. The present invention contemplates the detailed description of the invention. us n materials which will p s rve h pr par d It is well known in the art of electrochemical ,5 f th r i l lgi g g :J lontg pgi izds recording that a mark may be obtained by the o lme p or 0 mar mg. so con em a .es electrolytic deposition of a metal, such as silver, Storage of th p p e pp t In a uh dor in of colored compound, such as l peroxide: or order to maintain its moisture content withinthe of an adsorption complex, such as starch-iodme, Optimum fl until e tlme o e o d g- A on a paper support or other suitable carrier. It is ta le hlmi der 1s d SCl0s8d in Patent -1 Io. less commonly known that a the speed of re- 2,111,776, entltled Recording p p r Sys e 15- cording is increased, most of the materials which Sued 011 March 22, 1933, to n V- Hogan.- are satisfactory at lowtilpiedtbeloonig 1113561888. b1 i ggs 2 5:2 czlllg glggsrglgs is; tllllgegrozintnigfi While it may seem a i s on e possi e to compensate for the decrease in deposition time p d electrolytic recording on p t ted S D- by a proportional increase in current, so that the P Among the ammatlc bodies which have work done is the same regardless of the elapsed been found sgiitabie for use, according o he time, practical considerations definitely limit the present g 2 grexthose which have 11 1 extent to which this compensating current in- 93 55f; g g i 3 e crease may be utilized under any given conditions. g i j g c g g s Among the major limiting factors is current 49 8 hydroxy acldgs s bee}! g g i density which must be kep wen below the Point carriers impregnated with these lake-forming ma at which thermal decomposition of the sensitizing tenals will keep without discoloration fbr g ingredients, or of the carrier occurs. Another periods of time if Sumcienfly acid Thbse which factoris-electrode overvoltage, which does not are not sumciently acid in themselves may be necessarily ncrease at the same rate as does the kept by adding a Source of hydrogen ions more cungm t a mince oxldation or highly ionized than the lake-forming compound, f mtenslty that reqmred to profmce such as an acid which is stronger than the lake- Smtfime change o color j not be leached forming material. The quantity of acid must be until thermal decomposition 1s appreciab1e, and Such that the impregnatodsupport is maintained, loss of detailand other undesirable effects rewithout discoloration prior to marking but it Sultmust be insufficient to bleach the desired marks 9 The materlals a d processes o the present afterrecording. The electrolytes which are suitvention are suitable for recording with an efable for use in the present recording process are fective recording electrode area of 0.0001 square those which form strong bases under the action inch moving with a linear speed of thirty inches a second or more. i

It has been found that impregnation of the carrier just prior to marking has a number of of th recording current. The hydroxyl ions thus formed appear inthe record support at the electrode opposite the marking electrode and diffuse thru the support, neutralizing the acid at the point of marking, thus permitting the color lake to form. Too much acid cannot be properly neutralized. A slight excess of acid may be taken care of by raising the recording current thereby generating more hydroxyl ions, but the sensitivity is thus reduced,

It has been found, according to the present invention, that the added acid has an important and unexpected result in that it greatly increases the sharpness and detail of the final record. To accomplish this result, the acid in the support must be present in sufllcient amount to remove any fringes from the mark, but insuflicient to damage the mark itself. This has been found to be possible, since the amount of lake formed in the fringes is very much less than that in the desired mark. Hence, while some of the mark may be bleached by the acid, enough remains to give to the eye of the observer the impression of completeness, whereas the fringe is apparently entirely removed. This leaves the colored deposit only in the area of maximum density, which is the area directly under the recording electrode at the instant of the passage of recording current. The fringe is apparently due-to the ions which do not move directly thru the support upon the passage of current, and also to subsequent diffusion.

The amount of acid necessary to accomplish the above result will vary somewhat with the nature of the acid, the concentration of the electrolyte, and the marking current. The current in turn, is dependent upon the thickness and density of the paper, the moisture content, and the tinctorial power of the lake that is being formed. In general, 2 to 4 percent of the weight of the solid materials or 0.5 percent of the liquid,

of acid of the strength of oxalic acid or an amount of other acids chemically equivalent to this maybe used.

It has been found that when parchment type paper is used, a very thin sheet is suitable, because of its density and high wet-strength. A suitable grade is 0.0025 inch thick. For this type of paper, it has been found that a 20 percent solution of a uni-univalent electrolyte, such as sodium chloride, potassium chloride, sodium nitrate or potassium nitrate may be used with about 0.5 percent of an acid, such as oxalic or maleic for the purpose of preventing fringes. Any acid may be used as long as it is strong enough for the purpose and not so strong that it substantially weakens or discolors the support when in the quantity used.-

The ingredients of the preferred impregnating material, according to the present invention, are: a lake-forming aromatic compound, an electrolytically conductive salt of a strong base, an acid more highly ionized than the lake-forming aromatic compound, and water in proper proportions.

As a particular example, a sheet of parchment paper is impregnated with the following materials:

Pyrocatechin --grams.. 5 Sodium nitra do 5 Potassium chloride do 5 Oxalic acid n 0.5 Water cubic centimeters-.. 100

. A convenient method of impregnation is to assess-z pass the sheet thru a bath made up of the above. The moisture is allowed to distribute itself evenly throughout the paper. This takes several hours in the case of parchment paper. The impregnated paper may be stored in a humidor until the time of recording. At the instant of recording, the impregnated support must contain sufllcient moisture for the hydroxyl ions to migrate from the back of the support to the front, in order that the acid at the point of marking may be neutralized and the color-lake formed. The moisture must not be too great or diffusion of the mark will take place and loss of detail will result. Recording is accomplished by scanning the prepared paper with an electrode at least partly composed of a lake-forming metal and passing a modulated recording current thru the electrode and paper, in accordance with the subject matter to be recorded.

Another impregnating solution, according to the present invention, may be made by mixing the following:

Still another impregnating formula is as follows:

Sodium naphthol disulfonate 1:2:6 grams 10 Potassium nitrate do 10 Phosphoric acid do 0.5 Water cubic centimeters" found that increased detail in the record may be obtained by alloying a hardening metal with the above lake-forming metals. One of the best alloys has been found to be stainless steel containing about 5 percent molybdenum. The molybdenum lakes are light colored and hence this metal may be used in the recording electrode to increase detail and decrease the rate of solution of the electrode without appreciably altering the color intensity of the final record.

According tothe present invention, the impregnating material includes pplyhydroxy phenols in which at least two hydroxyl groups are in the 1: 2 position, or a combination, such as an ortho amino phenol, or acetylated amino group, is converted during the electrolysis of recording to a hydroxy body which will form a lake. Substituted di hydroxy phenols, such as their sulfonic acids, amino compounds, chlor or brom derivatives, are also suitable, as are the mono and di'carhoxyllic acids, and their homologues. In short, it has been found that substituent groups do not affect the lake-forming properties, provided the more acid substituents are converted in part, at least, to their salts. in order that this acidity be not so great that lake formation is hindered to an undesirable extent. Typical of the homologues are methyl di hydroxy benzene and naphthalene di-ol.

hence the highest conductivities. Thus, the

chlorides, bromides, and nitrates of caesium, rubidium,potassium, sodium or lithium are to be preferred. Less desirable, but still usable, are salts which have reducing properties, such as sulfites and thiocyanates, since the recording process includes oxidation at the anode and with these salts someof the recording power goes to oxidize their ions.

We further prefer salts whose ions, both positive and negative, are easily confined to the area in which they are discharged, so as to limit lateral diffusion. The chloride and nitrate ions confine their attack upon the recording electrode to a very small area, whereas the sulilte ion tends to diffuse its attack. Similarly, ammonium salts are found to be very undesirable, because the ammonium ion, when discharged, forms gaseous NH3 which diiluses over a relatively wide area,

forming ammonium hydroxide in locations that may be quite remote from the point of discharge. This diffusion causes fringes to form, and may leave insuflicient OH ions at the desired marking point to neutralize the acid, so that the color lake cannot form properly.

It has been found, according ot the present invention, that high speed recording requires suflieient lake-forming aromatic compound in the prepared support to yield a good mark. This requirement is met if the lake-forming aromatic compound has sumcient solubility in water. It hasv been found that a solubility 013 percent or greater in water at degrees centigrade is suiflcient.

g 3 The finished record keeps best when dry. The

impregnated support may be allowed to dry naturally after recording or artificial means may be 'used, such as a heater ora draft of air. The

heat generated by the recording current may also be utilized to speed drying. In addition, there cording electrode may be heated by means of an auxiliary heating current, so that the record emerges from the recording point in a substantially dry condition.

While only a few examples have been given, according to the present invention, its many possible modifications will be evident to those skilled in the art within the spirit and scope of the invention, as set forth in the appended claim.

What is claimed is: a

An electrolytic recording material, for recording by means of an electrode containing lakei'orming metal, said recording material being carried by an inert support, said recording material consisting essentially 01' an aqueous solution 01' at least one non-volatile electrolyte chosen from the group consisting of chlorides, bromides and nitrates or caesium, rubidium, potassium, sodium or lithium for conducting an electric recording current, at least one lake-forming 'polyhydroxy phenolic compound for combining with the metal electrode to form a colored mark, and at least one acid chosen from the group consisting of oxalic and maleic in quantity of about two to four per cent oi the solid matter in said recording ma terial for preserving the record, said composition being substantially free from lake-forming metals. I

' JOHN. V. L. HOGAN.

HUGH C. RESSLER. WILLIAM H. "I'RIBBLE. I 

